Nutrient Status Of Cells Research Articles

Carbon and nitrogen acquisition by the toxic dinoflagellate Alexandrium tamarense in response to different nitrogen sources and supply modes

Alexandrium tamarense was exposed to increasing nitrogen (N) concentrations from three sources; nitrate, ammonium and urea and two supply modes—pulsed and continuous, and its carbon (C) and N uptake kinetics were examined. Cellular properties and nutrient status of cells were found to be dependent on the type of supply, viz. pulsed vs. continuous. The type of N source and the supply mode induced variability in the C and N assimilation and their interaction. Both the supply mode and concentration of N were important in explaining the observed variability in cellular C and N uptake. Moreover, it was found that A. tamarense had the ability to take up substantial amounts of nitrate, ammonium and urea in the darkness. The present study showed that the changes in the C:N uptake ratios were dependent on the N supply mode rather than the nutrient status of cells. Variability in the C:N uptake ratios indicated unbalanced growth and this kind of uptake–growth strategy could be viewed as an ecological advantage in maintaining uninterrupted growth when nutrients are not supplied continuously. Evaluation of the uptake dynamics of A. tamarense in response to N conditions and the supply mode, enhance our understanding of how anthropogenic activities in global coastal regions can play an important role in controlling the nutrient uptake of this toxic dinoflagellate, and provide insights into the duration of a bloom.

Quantum yields of phytoplankton photosynthesis in the Gulf of Aqaba (Elat), Northern Red Sea

The Gulf of Aqaba (Elat) is characterized by oligotrophic waters and low productivity conditions in summer, when the euphotic zone of the stratified water column is severely nutrient-depleted. Winter is moderately productive, when mixing injects nutrients into the lit upper waters. The annual phytoplankton cycle and the bathymetric distribution of biomass and photosynthetic activity in the Gulf are analyzed in conjunction with the harvesting and utilization of light by cells. The harvesting of light energy at any depth is shown as an interaction between the optical properties of cells, a*, and the intensity and spectral distribution of the underwater light field. The efficiency by which phytoplankton cells utilize the absorbed light energy is the quantum yield of the photosynthetic process, Φ. The efficiency of light utilization by phytoplankton depends on the nutrient status of cells, their photoacclimation to ambient light, and the irradiance to which they are exposed. We show that the seasonal and spatial changes in the quantum yield of photosynthesis control the wax and wane of the different phytoplankton assemblages in the Gulf, thereby ultimately determining the flux of energy fueling all of the Gulf's planktonic and benthic biota.

Impact of Solar Ultraviolet Radiation on Marine Phytoplankton of Patagonia, Argentina¶

ABSTRACTPatagonia area is located in close proximity to the Antarctic ozone “hole” and thus receives enhanced ultraviolet B (UV‐B) radiation (280–315 nm) in addition to the normal levels of ultraviolet A (UV‐A; 315–400 nm) and photosynthetically available radiation (PAR; 400‐700 nm). In marine ecosystems of Patagonia, normal ultraviolet radiation (UVR) levels affect phytoplankton assemblages during the three phases of the annual succession: (1) prebloom season (late summer‐fall), (2) bloom season (winter‐early spring) and (3) postbloom season (late spring‐summer). Small‐size cells characterize the pre‐and postbloom communities, which have a relatively high photosynthetic inhibition because of high UVR levels during those seasons. During the bloom, characterized by micro‐plankton diatoms, photosynthetic inhibition is low because of the low UVR levels reaching the earth's surface during winter; this community, however, is more sensitive to UV‐B when inhibition is normalized by irradiance (i.e. biological weighting functions). In situ studies have shown that UVR significantly affects not only photosynthesis but also the DNA molecule, but these negative effects are rapidly reduced in the water column because of the differential attenuation of solar radiation. UVR also affects photosynthesis versus irradiance (P vs E) parameters of some natural phytoplankton assemblages (i.e. during the pre‐ but not during the postbloom season). However, there is a significant temporal variability of P vs E parameters, which are influenced by the nutrient status of cells and taxonomic composition; taxonomic composition is in turn associated with the stratification conditions (e.g. wind speed and duration). In Patagonia, wind speed is one of the most important variables that conditions the development of the winter bloom by regulating the depth of the upper mixed layer (UML) and hence the mean irradiance received by cells. Studies on the interactive effects of UVR and mixing show that responses of phytoplankton vary according to the taxonomic composition and cell structure of assemblages; therefore cells use UVR if >90% of the euphotic zone is being mixed. In fact, cell size plays a very important role when estimating the impact of UVR on phytoplankton, with large cells being more sensitive when determining photosynthesis inhibition, whereas small cells are more sensitive to DNA damage. Finally, in long‐term experiments, it was determined that UVR can shape the diatom community structure in some assemblages of coastal waters, but it is virtually unknown how these changes affect the trophody‐namics of marine systems. Future studies should consider the combined effects of UVR on both phytoplankton and grazers to establish potential changes in biodiversity of the area.

Impact of Solar Ultraviolet Radiation on Marine Phytoplankton of Patagonia, Argentina

Patagonia area is located in close proximity to the Antarctic ozone "hole" and thus receives enhanced ultraviolet B (UV-B) radiation (280-315 nm) in addition to the normal levels of ultraviolet A (UV-A; 315-400 nm) and photosynthetically available radiation (PAR; 400-700 nm). In marine ecosystems of Patagonia, normal ultraviolet radiation (UVR) levels affect phytoplankton assemblages during the three phases of the annual succession: (1) prebloom season (late summer-fall), (2) bloom season (winter-early spring) and (3) postbloom season (late spring-summer). Small-size cells characterize the pre- and postbloom communities, which have a relatively high photosynthetic inhibition because of high UVR levels during those seasons. During the bloom, characterized by microplankton diatoms, photosynthetic inhibition is low because of the low UVR levels reaching the earth's surface during winter; this community, however, is more sensitive to UV-B when inhibition is normalized by irradiance (i.e. biological weighting functions). In situ studies have shown that UVR significantly affects not only photosynthesis but also the DNA molecule, but these negative effects are rapidly reduced in the water column because of the differential attenuation of solar radiation. UVR also affects photosynthesis versus irradiance (P vs E) parameters of some natural phytoplankton assemblages (i.e. during the pre- but not during the postbloom season). However, there is a significant temporal variability of P vs E parameters, which are influenced by the nutrient status of cells and taxonomic composition; taxonomic composition is in turn associated with the stratification conditions (e.g. wind speed and duration). In Patagonia, wind speed is one of the most important variables that conditions the development of the winter bloom by regulating the depth of the upper mixed layer (UML) and hence the mean irradiance received by cells. Studies on the interactive effects of UVR and mixing show that responses of phytoplankton vary according to the taxonomic composition and cell structure of assemblages; therefore cells use UVR if >90% of the euphotic zone is being mixed. In fact, cell size plays a very important role when estimating the impact of UVR on phytoplankton, with large cells being more sensitive when determining photosynthesis inhibition, whereas small cells are more sensitive to DNA damage. Finally, in long-term experiments, it was determined that UVR can shape the diatom community structure in some assemblages of coastal waters, but it is virtually unknown how these changes affect the trophodynamics of marine systems. Future studies should consider the combined effects of UVR on both phytoplankton and grazers to establish potential changes in biodiversity of the area.